GEOL: CHAPTER 8

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GEOL CHAPTER 8

• Earthquakes and Earths Interior

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Learning Outcomes

• LO1 Explain Elastic Rebound Theory
• LO2 Describe seismology
• LO3 Identify where earthquakes occur, and how
  often
• LO4 Identify different seismic waves
• LO5 Discuss how earthquakes are located

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Learning Outcomes, cont.

• LO6 Explain how the strength of an earthquake is
  measured
• LO7 Describe the destructive effects of
  earthquakes 
• LO8 Discuss earthquake prediction methods
• LO9 Discuss earthquake control methods

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Learning Outcomes, cont.

• LO10 Describe Earth's interior
• LO11 Examine Earth's core
• LO12 Examine Earth's mantle
• LO13 Describe Earth's internal heat
• LO14 Examine earth's crust

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Earths Interior

• Crust
• Mantle
• Outer core
• Inner core

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Seismic Waves and Earths Interior

• P-wave and S-wave velocity determined by density
  and elasticity of material
• S-waves dont travel through liquids
• Seismic waves change velocity and direction when
  enter material with different density or
  elasticity (refraction)

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Seismic Waves and Earths Interior, cont.

• Some waves are reflected
• Calculate depths of boundaries
• Discontinuity significant change in materials or
  their properties

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The Core

• P-wave velocity decreases at a depth of 2,900 km
  core-mantle discontinuity
• P-wave shadow zone
• Weak P-wave energy does penetrate the shadow
  zone from solid inner core
• S-wave shadow zone shows the outer core is
  liquid, because S-waves cant travel through
  liquids

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Core Density and Composition

• 16.4 Earth volume
• 33 of mass
• Outer core 9.9 to 12.2 g/cm3
• Earth center pressure 3.5 million times of
  surface
• Outer core iron, sulfur, silicon, oxygen,
  nickel, potassium
• Inner core iron and nickel

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Earths Mantle

• Moho discontinuity about 30 km deep
• Asthenosphere
• 100-250 km deep
• P- and S-waves slow down
• Plastic
• Magma generation
• Lithospheric plates ride across it
• 3.3 to 5.7 g/cm3 probably periodotite

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Earths Internal Heat

• Geothermal gradient 25ºC/km
• Greater in active volcanic regions
• Most heat generated by radioactive decay
• Regions of equilibrium temperature
• Base of crust 800ºC to 1200ºC
• Core-mantle boundary 2,500ºC -5,000ºC

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Continental Crust

• Granitic composition
• 2.5 to 3.0 g/cm3 average 2.7 g/cm3
• 20 to 90 km thick average 35 km thick
• Thickest under large mountain ranges

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Oceanic Crust

• Gabbro overlain by basalt
• Average density 3.0 g/cm3
• 5-10 km thick
• Thinnest at spreading ridges